A drive by President François Hollande to legalise gay marriage is shaping up as an epic battle between left and right but also between urban France and 'La France Profonde'.

The leader of the main centre-right opposition party, Jean-François Cope, provoked a storm of criticism when he called for street demonstrations against all left-wing projects that threaten the "pillars of our society".

Separately, rural politicians -- not all of them on the right -- are campaigning for "a conscience clause", which would allow the mayors of towns to refuse to perform same-sex marriages when they become legal, as expected, early next year.

A draft law is expected to go before the government next week to allow marriages between same-sex couples. The law would also abolish "mother" and "father" as legal terms and recognise only "parents".